1. Field of the Invention
The invention relates to remove silicon oxynitride on semiconductor substrate, more particularly to remove silicon oxynitride without effecting the shape of the gate portions.
2. Description of the Prior Art
Using silicon oxynitride (SiON) as the bottom anti-reflection coating layer for the deep sub-micro device is the well-known process to SRAM technique. Normally, the conventional process can be indicated as the following statement.
First of all, FIG. 1A shows that there semiconductor substrate 10, gate oxide 11, undo-type polysilicon 12, N+ type polysilicon 13 and silicon oxynitride 14 are all provided.
Then, silicon oxynitride 14 is removed by the, hot H3PO4 solution as FIG. 1B. However, unfortunately it is found at this step that the implanted N+-type polysilicon gate will be damaged by the hot H3PO4 solution. Especially, shape of the implanted N+-type polysilicon gate is not shown as the purpose shape.
Thus, a new improvement technology is indeed necessary according to the above statement.
In accordance with the present invention, a method is provided for removing silicon oxynitride that substantially keeps the purpose shape of the underlying gate.
In one embodiment, a method for removing silicon oxynitride of polysilicon gates in fabricating integrated circuits will be the following. A semiconductor substrate is provided over which a doped polysilicon gate and an undoped polysilicon gate are formed, and an oxynitride layer used as an anti-reflective coating (ARC) is formed on the surface of the polysilicon gates. Then, a photoresist layer is coated over the substrate and the oxynitride layer. A reverse mask is utilized to remove the photoresist on a major portion of the surface of the undoped polysilicon gate. A portion of the photoresist layer is etched back such that the sidewall and surface of the oxynitride layer are exposed. The oxynitride layer is dry etched, wherein the doped and the undoped polysilicon gates are protected by the remaining photoresist layer while removing the oxynitride layer. The remaining photoresist layer is removed until the surface of the substrate is exposed. Finally, the surfaces of the doped and the undoped polysilicon gates and the substrate are all cleaned.